SCOTUS & Congress has confronted the Agency about it numerous times and President Ford. See the post or two above. Wikepedia has several pages- sourced on MKUltra. It was an expensive and extensive program, too big too hide.
> It was an expensive and extensive program, too big too hide.
Two of the three assertions in that sentence are not supportable. The Wiki article indicates it cost less than $100 mil in inflation-adjusted dollars; you could sink a program like that into the CIA black budget without a problem.
And if they hid the mass surveillance programs as long as they did, they can surely hide something like this.